Investment Securities - Schedule Of Available-For-Sale Securities Proceeds, Gains, And Losses (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Marketable Securities [Abstract]
Proceeds	$ 24,102nrim_AvailableForSaleSecuritiesProceeds	$ 23,514nrim_AvailableForSaleSecuritiesProceeds	$ 21,382nrim_AvailableForSaleSecuritiesProceeds
Gross Gains	465	333	419
Gross Losses	$ 4	$ 0	$ 0

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration